Cellulosic pellicles and methods for producing same



Patented Aug. .29, 1-939 um'rso STATES PATENT OFFICE 'OEliLULOSICPELLICLES AND METHODS FOR PRODUCING SAME William Frederick Underwood,Buffalo, N. Y., and

Henry S. Rotliroc Wilmington, Del., assirnors,

by meme assignments,- moors a Company, Wilmington,

notation of Delaware No Drawing. I

zzcnims.

tions.

Cellulosic pellicles which are obtained by coagulation or precipitationfrom aqueous or alkaline aqueous dispersions of cellulose or cellulosederivatives, as for example pellicles of regenerated cellulose, glycolcellulose, cellulose glycolic acid,

lowly etherlfled or esterifled cellulose such as lowly etherified methyand ethyl cellulose and lowly esterlfled cellulose acetate, areparticularly useful as wrapping materials. It is essential, however,that these pellicles be flexible and further that this flexibility bemaintained. Cellulosic pellicles of this character seem to depend on thepresence of moisture to impart flexibility and the softeners which havebeen used heretofore have been selected because of their hyg oscopicnature. It has been considered necessary to have the softener assist, byvirtue of its hygroscopicity, in the retention of a suitable amount ofmoisture although the softener has possessed, also, a certain degree oflubricating or plasticizing action so that the pellicle does not becometoo brittle when practically all of the moisture has been removed. Inthe absence of a softener other than water, these pellicles become sobrittle when dried as to be substantially useless as wrapping tissues.In the presence of the hygroscopic softeners of. the prior art, the lossof moisture is retarded and generally speaking, the flexibility ismaintained by the.

moisture present.

Regenerated cellulose pellicles (for convenience the invention will bedescribed in terms of this species), are quite sensitive to changes inmoisture content, not only as regards flexibility, but also as regardsdimensions. Increase in moisture content causes-a swelling of thecellulosic structure, while decrease in moisture content causes ashrinking apparently due in part to collapse of the cellulose micellesand in part to the loss of water molecules from between the micelles.

Regenerated cellulose wrapping tissues are subject, therefore, to twomajor defects which develop simultaneously and which are primarilydependent on the softener, namely embrittlement and deformation.Previous attempts to control or prevent embrittlement, however, have notbeen successful in controlling the deformation for, as mentioned above.the softeners selected have been highly hygroscopic and havereallyresulted in greater sensitivity to moisture conditions, therebyincreasing the expansion and contraction of to E. I. du Pont de Ne- DeL.a cor- Application January 4, 1936, Serial No. 57,634

wrapping tissues or similar pelllcular structures,

Thus it is that great care is required in wrapping boxes in regeneratedcellulose pellicles to provide. for these conditions. For example, if acereal box is wrapped in regenerated cellulose sheeting (prepared inaccordance with the prior commercial methods and softened with glycerinwhich is the usual hygroscopic softener) and set aside for storage, itmay be subjected to a variety of humidity conditions before it reachesits ultimate consumer. During this time, if the humidity is high, theregenerated cellulose may expand untilthe wrapper becomes loose aroundthe box and in some cases even baggy and wrinkled. On the other hand, ifthe humidity is low, loss of moisture from the regenerated cellulosewill cause the wrapper to contract and this may cause buckling of thebox walls, or if the box is sufliciently rigid, the wrapper itself mayburst. Thus, under such a variety of humidity conditions, packageswrapped in regenerated cellulose sheeting may have an unsightly andundesirable appearance as the result of the deformation of theregenerated cellulose. Obviously, this defeats the .very importantpurposes of regenerated cellulose wrappers which are intended to protectand beautify articles wrapped therein.

To overcome the troublesome deformation, wrapping machinery has beendesigned to allow for a certain slack or looseness in the wrap. This,obviously, will eliminate the effects of contraction, but cannot, helpthe expansion effects; indeed, it makes them worse. The use ofmoistureproofed regenerated cellulose pellicles does not eliminate thetrouble because the application of a moistureprooflng coatingretards butdoes not prevent the deformation, which latter is, in'the ultimate, notappreciably affected. These practical means do nothing more than attemptto make the best of the situation and make use of regenerated cellulosesheeting as it is available. No attempt is made to change the inherentproperties of the cellulosic material and so provide a. wrapping whichwill have improved properties and characteristics.

It has been found in the manufacture of regenerated cellulose pelliclesthat the degree of deformation is, at least in part, due to theorientation of the cellulosio micelles. Thus, if a sheet of regeneratedcellulose is made in such a way as to provide substantially uniformtension in all directions, the degree of deformation will besubstantially the same in all directions. Practically, however,regenerated cellulose pellicles are made in a continuous process whereinthe pellicle, after This results in an-appreciableJdifferenjce in thedegree of deformation if measured in the machine direction, as comparedto the degree of deformation if measured at right angles to the machinedirection, 1. e., the transverse'direction.

However, in any given process the conditions are such that the degreesof deformation in the machine and transverse directions usually bear asufficiently constant relationship so that for test purposesit isusually suflicient to determine the degree of deformation in onedirection only, usually the machine direction.

For the purposes of this specification the degree of deformation, whichmay be called simply f deformation, is the per cent change in length ofa cellulosic pellicle as measured in the machine di-' rection inaccordance with the followingQproce dure: Strips of material areallowedto come to.

equilibrium withan atmosphere of substantially 95% relative humidity ata temperature "of35 C.

and their length accurately measured. The strips are then allowed toreach equilibrium in an atmosphere of substantially 0% relative humidityat the same temperature and their length again accurately measured. Thedifference in length divided by the length as originally measuredmultiplied by 100 gives theper cent deformation over the given humidityrange at 35 C. and flgures so obtained are conveniently called thedeformation. Thus, a sample strip having an original length of 10 inchesand a contraction in length of 0.42 inch would be said to have adeformation of 4.2.

It is the object of this invention to provide means for reducing thedeformation of cellulosic pellicles. It is also'an object of theinvention to effect simultaneous softening and reduction of deformation.It is a further object to provide a method whereby the aforementionedobjects may be accomplished in an economically feasible manner andwithout entailing essential modification of apparatus customarily usedin the manufacture of such pellicles.

More specifically, it is the object of the invention to provide meansfor the production of cellulosic pellicleswhich will show lessdeformation than the cellulosic pellicles presentlyv commerciallyavailable. I

Specifically, it is the object of the invention to produce a pellicle ofregenerated cellulose suitable for use as a wrapping tissue which willshow a degree of deformation of not in excess of 3.0 when tested inaccordance with the method described above. This object also includesthe production of a regenerated cellulose pellicle which is combinedwith a softening material and which shows a deformation not in excess of3.0.

The above and other objects of the invention may be accomplished byimpregnating into the cellulosic pellicle, preferably while the latteris in a wet or gel state, an appreciably water-soluble, highboiling (i.e., relatively non-volatile at ordinary temperatures and j pressures),limitedly hygroscopic material which is stable, essentially colorlessand odorless, preferably non-toxic ,and which is preferably also asoftening agent for the cellulosic material. The extent of the reductionin deformation which may be obtained depends a temperature of 25 .notnecessarily liquids.

on the particular impregnant used and to a certain extent on the amountemployed.

The term limitedly hygroscopic is intended to include substances whichwill absorb 1-80% of their weight of water when exposed alone in a thinlayer to an atmosphere of substantially relative humidity at atemperature of '25 C. over a period of hours. The test forhygroscopicity is carried out as follows: A small sample of about0.5-2.0 grams of thoroughly dried material is spread evenly over thebottom of a weighing bottle (conveniently about 2%" in diameter and 115" deep) and the weight of the sample acthen placed in a chamber inwhich an atmosphere of substantially 95% relative humidity and C. aremaintained. The humidatmosphere may be maintained conveniently by meansof a sulfuric acid solution (9 parts of water to 1 part sulfuric acid)contained within the chamber. The sample, after 120 hours exposure,-during which time the material is occasionally agitated as by gentlytipping the container to cause the material to flow over the bottom ofthe weighing bottle, is r'eweighed accurately and the percentageincrease in weight based on the original weight of the sample representsthe hygroscopicity of the material. Thus, if 1 gram of a substanceabsorbs 0.25 gram of water under the conditions described, it will besaid to have a hygroscopicity of 25.

,curately measured. The open weighing bottle is' The test forhygroscopicity as outlined above is satisfactory for determiningwhether. or not a given substance is suitable for the purposes of theinvention. There may be other tests of equal utility for determininghygroscopicity which would give different numerical values. Obviously,

such methods should be calibrated against the method outlined if theyare chosen for use. Based on the method described, those substancessuitable for use in the practice of the invention will have ahygroscopicity of 1 to 80.

Generally speaking, the test of water-solubility is applied first todetermine the suitability of substances for use in the practice of theinvention. If the substance is at least 1% and not more than 40% solublein water at 20 C. its utility is indicated. In the case where thesolubility is more than 40%, the hygroscopicity should be determined andin the event that this value should be above 80, the substance will beuseless for the purposes of the invention.

' The third physic'al criterion relates to volatility. The substancesmust be high-boiling, that is, substantially non-volatile at ordinarytemperatures and pressures, and should be preferably though Obvously, ifsubstances of appreciable volatility were to be used, they wouldeventually disappear from the cellulosic pellicles rendering themthereby brittle, fragile and unsuitable for use as wrapping tissues orother applications. It has been found that substances of appropriatewater-solubility and hygroscopicity which have a boiling point of C. orhigher, at a pressure of 12 mm. of mercury and preferably of C. orhigher (at 12 mm.) will be suitable for use.

In the preferred form of the invention substances having limitedhydroscopicityand appropriate boiling-point and which are at least 4%soluble in water at 20 C. will be used to impreg'nate the cellulosicpellicles to effect a reduction in deformation. Substances of thischaracter may be introduced into the pellicles by increase theconcentration by adding a watermeans of. a simple water solution. In"the case where it is desired to uses. substance which is less than 4%soluble, it may be convenient to miscible organic solvent such asmethanol, ethanol, acetone or the like although in no case should morethan 25% by volume-of such solvent in the water-solvent mixture benecessary. Substances which require more organic solvent are unsuitedfor.- the purposes of the invention. In.- asmuch as the use of a portionof organic solvent entails additional expense, it is desirable to usethose substances which are at least'4% soluble although the less solublesubstances will find many useful applications.

Although the principal objective of the invention relates to thereduction of deformation, it is a part of the invention to provide alsoa -fiexible .pellicle. This can be done frequently by proper choice ofthe impregnating agent so that it will be at one and the same time asoftener and a deformation reducing agent. For simplicity, such an agentmay be termed a nondeforming softener. Obviously, other properties maybe combined with these in certain agents, which will have particularadvantage.

Generally speaking, compounds of the following types will serve asnon-deforming softeners for cellulosic pellicles such as regeneratedcellulose: organic compounds containing (a) both ether and ester, groups(called for convenience ether-esters"), (b) both keto and ester drcxylgroup for each ester group (conveniently a called "hydroxy-esters"), and(d) compounds of carbamic acid esterified with an alcohol containing anether group. As a general rule, compounds of these types wherein thehydrocarbon 5 portions are straight chain will be more effectivesoftening agents than those wherein the-hydrocarbon portion is branchedchain or cyclic.

Among the substances which may serve as non-deforming agents wheresoftening action is 10 not important, the following types may be men- 1As illustrative of specificmaterials which are 'useful in the practiceof theinvention, a number of compounds are listed in the followingtable, together with data as to water-solubility and deformation, thelatter figures being obtained 30 when regenerated cellulose pellicleswere impregnated as will be described in more detail below.

Table I Approximate water solubility at 20 C.

Deformatlon A. Ether-esters:

. 1. Ether-alcohol derivatives (alcohol radical contains an ethergroup):

a) Bis-ethoxyethyl b Bisyethyl ii (I) Bis-ethoxyethyl m (c) Bis-ctoxyethyl diglyco nis-butox em idl l eouml' (e Glycerol trl-[methoxyacetate]. (D Diethylene glycol dl-[alphe-methoxy B. Ketoaters' (a)Propylene gl col di-[levullnate].-

Diethylene g ycol di-[lcvulinate]; (c) Butoxy-ethoxyethyl levulinate---Ethylene glycol di-[levulinate] Trimeth lone glycol di-[lcvuhnate].

C. Hydroxy esters:

' (a) Bisethoxyethylmelate.--

ene glycol di- Glycero trl-[levulinate (as Propionate ofbis-methoxyethyl malato Acetate oi bis-methoxyethyl mailma (e) Acetateof bis-ethofi'etgyl malate.

conteinsan th gm (b) Butoxy-ethoxyethy Bis-propoxyethyl malate" (c (d)Ethoxyethyl tertmm lb t l (I) Methcxyethyl Bis'beta-hydroxycthylbeta-hydroxyet'hyl phthalate hthala V D. Cami. eel esters:

(c) Butoxy-ethoxyethyl carbamate ..-l

-ethcxyethyl carbemate.

Iso-buto (b ((3; Butoxyet yl cm a. amides:

- F. Other Agen Ethoxy-ethoxyethyl carbamate (a) N-bcta-hydroxyethy]p-toluene 110mm 187 (b) gipiperldyl dlmethyl urea o (a Monoethyl otherolhexamethylene glycol. (b 2-Hydroxy-cyclohcxylether oi dietbyleneglycol (c 2-Hydroxy-cyolohexyl other of glycol-01.;

Very 61685;

Mlsclble. Miscible. Mlscible w re w s m s s wrs p s s m s s m 00 cm: uoomawarocaw saom-waq-aua NHHWQH- QOINI- WN -.1

groups with or without ether groups (conveniently called keto-esters),(0) both hydroxyl and ester groups with or without ether groups. butwhich do not contain more than one ,hy--,

The compounds listed in Table I are representative and it is to be notedthat simple organic chemical compounds are elfective for the purposes ofthe invention. All of the substances 75 manufacture of present-daycommercial regenerated cellulose sheeting. 'lhus,- a sheet of gelregenerated cellulose which has been purified and washedis impregnatedwith an aqueous glycerol solution, the excess of such solution removedby suitable means and the sheet dried. The commercial operation iscontinuous and the time of immersion in the glycerol bath varies withthe speed of the machine although about 20 seconds immersion is probablynormal. The concentration of the glycerol in the bath is adjusted toleave a predetermined amount of glycerol in the sheet after the dryingoperation, which latter removes all but about 68% water, based on theweight of the cellulose; Generally, the amount of glycerol in the finalproduct is of the order of 15% and it has been found that a bathcontaining about 4-6% glycerol will give the desired results.

Accordingly, in the practice of the present invention the gel pellicleis impregnated with a bath which may contain conveniently about Mitt; ofthe non-deforming agent. After removal of excess bath, as by squeezerolls and the removal of excess water by drying, the final product willcontain a suitable amount of nondeiorming agent. Obviously, the amountof aaent in the final product will be adjusted to unit desiredproperties expected in the sheet so that the bath concentration may bemore or less than 4% as occasion demands. Kt found however that theeffectiveness of most non-deforming agents appears to approach alimiting value so that excessive amounts do not produce sumcientimprovement to justify their use. Usually a bath concentration of aboutl% will be found satisfactory for a realization of good non-deformingproperties and at the same time economy oi operation. Where the is to beused at low temperatures and low hnmidities, 21.6% solution may be foundadyantaseous.

a specific example, a gel sheet of regenerated cellulose may beimpregnated with a 4% aqueous solution of bis-ethoxyethyl malate. Theresultant sheet, after dryinil, shows'a deformato'nof about 2.3, whereasa similar sheet impregnoted with glycerol showsa deformation of 4.9M.Both sheets contains approximately.

'es iecially'suitable for use there are a number of hydroxy esters.These may be obtained by the estleriflcation of hydroxy acids such asmalic, l ic, glycollic, tartaric, alpha-hydroxy butyric,

haric, gluconic, or the like with alcohols or ether-alcohols which maybe monoor polyhydric. If polyhydric alcohols are esterifled withpolybasic acids, the proportions of reactants and the method ofesteriflcation are chosen so that resinous products are not ob tained.Hydroxy esters may be obtained also by the partial csteriflcation orpolyhydric alcohols with carboxylic acids of all kinds, such as acetic,propionic, succinic, adipic, phthalic or the like in which case thealcohol portion of the ester furnishes the hydroxyl group. Similarly, apolybasic acid may be esterifled partially by means of a monohydricalcohol and partially by means of a polyhydric alcohol so as to have atleast one tree hydroxyl group in the final molecule. Only thosehydroxy'esters, however, which satisfy the required criteria ofnon-volatility, solubility, and hygroscopicity are useful for theinvention.

Amides or substituted amides of organic carboxylic or sulfonic acids maybe used. This includes amides of all types of organic carboxylic acidswhich may contain, attached either ,to carbon or nitrogen, any type ofan organic group and which preferably contain ether groups in theirmolecules.

In the above table a large number of compounds has been indicated, eachof which is capable of use in the production of a regenerated cellulosepellicle which will show a deformation of not more than 3.0. It is to beunderstood that the compounds mentioned are illustrative. The list givenis by no means exhaustive and this disclosure is intended to embrace allorganic compounds or mixtures which have properties as previously setforth. These compounds may be used alone or in combination with eachother.

The hygroscopici-ty oi the compound chosen for use will determine, inlarge measure, the amount of reduction in deformation which will beobserved. Thus, compounds having a hygroscopicity of from 60 to 80 willshow in most cases a deformation of the order of 2.7 to 3.0, while ifthe hygrcscopicity is from to 60, a deformation of the order of 2.3 to3.0 will usuallybe obtained, and if the hygroscopieity is from 1 to 25,a deformation of about 2.3 or less (usually of the order of 2.6 to 2.3)will be achieved in most instances. Thus, it can. be seen that anyvariation in properties which may be desired in the finished product canbe secured by proper selection of a non-deforming agent or non-deformingsoftener in accordance with the principles set forth herein.

The cellulosie pellicles obtainable by means of the present inventionare particularly suited to wrapping purposes since the reduceddeformation substantially eliminates warping, swelling, wrin-v kling andbreakage. Similarly, the lamination of such pellicles to materials suchas paper or fabric is'iacilitated since there is less tendency for thelaminated product to curl, buckle or wrinkle. When stacks of sheets arestored, there is a lesser tendency for contiguous sheets to stick-acommon experience with glycerol-softened sheets. Generally, thedurability, particularly at low temperatures of 0 C. or less isimproved- The process described is especially advantageous from aneconomic viewpoint inasmuch as it offers a meth- 0d of producing thisnew type of cellulosic pellicle without alteration or presentmanufacturing equipment.

While it is preferred that the cellulosi'c pellicle be impregnated witha solution of the non-deforming agent while the pellicle is in the gelstate, i. e., before it is dried and while' it still contains a largeamount or water, it is within the broad scope of the invention toimpregnate a film which has been dried and then rewetted.

Although the invention has been described with specific reference tofilms of regenerated cellulose prepared by the viscose process since itis in this fleld that the invention is of greatest utility, it will beunderstood that the broad scope of the invention includes the treatmentof other types of cellulosic film cast from aqueous or aqueous alkalinesolutions. Thus, the non-deforming agents referred to above may be usedwith advantage in the treatment of films produced from cuprammoniumcellulose solutions, from aqueous alkaline solutions of glycol celluloseor cellulose glycollic acid,

from aqueous alkaline solutions of lowly etherified cellulose, e. g.,lowly etherified methyl cellulose or lowly etherified ethyl cellulose,or from aqueous alkaline solutions of lowly esterified cellulose, e. g.,lowly esterified cellulose acetate.

Since the invention is capable of considerable variation andmodification, any change from the above specific details and exampleswhich conforms to the spirit of the invention, is intended to beincluded within the scope of the claims.

No claim is made herein to the specific use of ether-esters, keto-estersand carbamic acid esters since this specific use is claimed inco-pending patent applications to Henry S. Rothrock, Serial Nos. 57,632and 57,633 and to Frederick M. Meigs, Serial Nos. 57,635 and 57,636.

We claim:

1. Water-sensitive film suitable for use as a wrapping tissue formedfrom an aqueous alkaline cellulosic solution containing, as adeformationrestricting agent, a softening agent for said film comprisingan organic compound having a hygroscopicity of from 1 to 80, a boilingpoint of at least 135 C. at a pressure of 12 mm. of mercury, and asolubility of at least 1% in water at 20 0., said, organic compoundbeing present in sufiicient quantity to restrict the deformation of thefilm to a maximum of 3.0.

2. Water-sensitive film as defined in claim 1 characterized in that saidorganic compound is a hydroxy ester.

3. Water-sensitive film as defined in claim 1 characterized in that saidorganic compound is bis-ethoxyethyl malate.

4. Water-sensitive film as defined in claim 1 characterized in that saidorganic compound is an amide. g

5. Water-sensitive film as defined in claim 1 characterized in that saidorganic compound N-beta-hydroxyethyl p-toluene sulfonamide.

6. Regenerated cellulose film suitable for use as a wrapping tissuecontaining, as a deformationrestricting agent, a softening agent forsaid film comprising an organic compound having a hydroscopicity of from1 to 80, a boiling point of at least 135 C. at a pressure of 12 mm. ofmercury, and a solubility of at least 1% in water at 20 C., said organiccompound being present in sufiicient quantity to restrict thedeformation of the film to a maximum of 3.0.

7. Regenerated cellulose film as defined in claim 6 characterized inthat'said organic compound is a hydroxy ester.

8. Regenerated cellulose film as defined in claim 6 characterized inthat said organic compound is bis-ethoxyethyl malate.

9. Regenerated cellulose film as defined in claim 6 characterized inthat said organic compound is an amide.

10. Regenerated cellulose film as defined in claim 6 characterized inthat said organic compound is N-beta-hydroxyethyl p-toluene sulfonamide.

11. A process for reducing the deformation ofwater-sensitive film formedfrom an aqueous alkaline cellulosic solution, which comprisesirnpregnating said film with an aqueous solution containing a sufilcientquantity of a deformationrestricting agent to restrict the deformationof the film to a maximum of 3.0, said deformation-- restricting agentbeing a softener. for said film and comprising an organic compoundhaving a hygroscopicity of from 1 to 80, a boiling point of at least 135C. at a pressure of 12 mm. of mercury, and a solubility of at least 1 inwater at 20 C.

12. A process for reducing the deformation of water-sensitive filmformed from an aqueous alkaline cellulosic solution, which comprisesimpregnating said film while in the gel state with an aqueous solutioncontaining a suificient quantity of a deformation-restricting agent torestrict the deformation of the film to a maximum of 3.0, saiddeformation-restricting agent being a softener for said film andcomprising an organic compound having a hygroscopicity of from 1 to 80,a boiling point of at least 135 C. at a pressure of 12 mm. of mercury,and a solubility of at least 1% in water at 20 C.

13. A process for reducing the deformation of water-sensitive film asdefined in claim 11 characterized in that said organic compound is aethoxyethyl malate.

15. A process for reducing the deformation of water-sensitive film asdefined in claim 11 characterized in that said organic compound is anamide.

16. A process for reducing the deformation of water-sensitive film asdefined in claim 11 characterized in that said organic compound is N-beta-hydroxyethyl p-toluene sulfonamide.

17. A process for reducing the deformation of regenerated cellulose filmwhich comprises impregnating said film with an aqueous solutioncontaining a sufficient quantity of a deformationrestricting agent torestrict the deformation of the film to a maximum of 3.0, saiddeformationrestricting agent being a softener for said film andcomprising an organic compound having a hygroscopicity of from 1 to 80,a boiling point of at least 135 C. at a pressure of 12 mm of mercury,and a solubility of at least 1% in water at 20 C.

18. A process for reducing the deformation of gel regenerated cellulosefilm which comprises impregnating said film with an aqueous solutioncontaining a sufilcient quantity of a deformationrestricting agent torestrict the deformation of the film to a maximum of 3.0, saiddeformationrestricting agent being a softener for said film andcomprising an organic compound having a hygroscopicity of from 1 to 80,a boiling point of at least 135 C. at a pressure of 12 mm. of mercury,and a solubility of at least 1 in water at 20 C.

19. A process for reducing the deformation of regenerated cellulose filmas defined in claim 17 characterized in that said organic compound is ahydroxy ester.

20. A process for reducing the deformation of regenerated cellulose filmas defined in claim 17 characterized in that said organic compound isbis-ethoxyethyl malate.

21. A process for reducing the deformation of regenerated cellulose filmas defined in claim 17 characterized in that said organic compound is anWILLIAM FREDERICK UNDERWOOD. HENRY S. ROTHROCK.

